Whole-body cryotherapy ― or the practice of submerging yourself into a deep-freezing tank ― has exploded in popularity over the past few years, especially among pro athletes and celebrities. Tons of gyms, spas and wellness centers now offer the treatment, claiming it can boost metabolism and ease symptoms of inflammation and pain for a long list of health conditions (like arthritis, fibromyalgia and migraines).

But not everyone is so sure about the practice. Some people believe it’s a potentially dangerous hoax, and others — like former Pittsburgh Steelers wide receiver Antonio Brown — have sustained frostbite injuries from the cold tanks. One woman was even found dead in a cryotherapy tank in Nevada a few years ago.

Given the major lack of evidence we currently have on whole-body cryotherapy, many experts are skeptical about its ability to heal and detox the body and warn people to think twice before walking into a tank.

What goes on in cryotherapy?

Whole-body cryotherapy, also sometimes called WBC or “super-cooling,” involves stripping down to socks and gloves and stepping into a human-sized chamber that’s set to about -200 degrees Fahrenheit or colder for two to four minutes. The skin temperature then drops, as does overall body temperature, both of which are largely dependent on the person’s gender, weight and fitness level.

Those who are pro-WBC claim the frigid temps constrict and then widen the blood vessels, which causes the body to release toxins and endorphins. This play on blood flow is thought to alleviate pain, boost metabolism, slow the aging process and have all sorts of healing abilities.

Most single sessions will cost you upward of $80, with a monthly membership being even more.

We don’t have too much research on cryotherapy.

Think of a time you got injured. You likely used a cold pack to numb the wound and ease the pain. Localized cooling treatments like that are known to reduce blood flow and lower pain levels, inflammation and swelling.

Whole-body cryotherapy is based on this same idea of utilizing cold as a therapeutic agent — but the evidence just isn’t there to back it up. And because WBC is not regulated by the Food and Drug Administration, the research we do have has mostly been conducted by private cryotherapy studios or practitioners who have a financial tie to it, according to Dr. Robert Shmerling, a rheumatologist and associate professor of medicine at Beth Israel Deaconess Medical Center.

In fact, the FDA states that “despite claims by many spas and wellness centers to the contrary, the U.S. Food and Drug Administration (FDA) does not have evidence that WBC effectively treats diseases or conditions like Alzheimer’s, fibromyalgia, migraines, rheumatoid arthritis, multiple sclerosis, stress, anxiety or chronic pain.”

The lack of regulation by the FDA also means that there’s no golden rule regarding the temperature and duration of cryotherapy. As a result, different wellness centers use different cooling technologies. This has made it particularly difficult to reliably study the effects of WBC, according to Erich Hohenauer, a senior researcher at the University of Applied Sciences and Arts of Southern Switzerland who has conducted research on cryotherapy.

Furthermore, the studies out there have predominantly looked at the effects in men, so it’s even more unclear how the treatment affects women, Hohenauer noted.

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Here’s what the science does say.

Two of the biggest studies — a report from 2014 and another from 2015 — looked at a total of 14 previous studies and concluded that there’s not enough evidence to say whether or not the cooling treatment has any significant impact on pain or muscle soreness. And though WBC may improve some people’s perception of recovery, the researchers determined it’s probably best to just use a local ice pack on any pain or soreness — we know that’s effective (and affordable), they said.

More recent research from 2017 evaluated 10 previous WBC articles and determined that patients often note improvements in pain, soreness, stress and post-exercise recovery. In some cases, WBC does seem to have anti-inflammatory effects — and the more often it’s done, the greater the effects. But, overall, the data is mixed: Many patients reported no improvements.

Some health experts suspect there may be a powerful placebo effect at play.

“For something subjective, such as pain ― rather than something objective, like the size of a tumor ― you can demonstrate that the expectation of benefit leads to benefit,” Shmerling said.

Shmerling said it may be similar to the phenomenon that happens with a sugar pill: In a study, if you tell some participants with pain they’re getting a powerful pain reliever and others they’re getting a sugar pill, more people in the first group will report pain relief.

“The same could be true for WBC: You tell people with migraines that it works great for headaches; they get in this horribly cold container for two minutes and some percentage of people will say they feel better,” Shmerling said.

Cryotherapy isn’t risk-free.

There are also some potential risks to be aware of with WBC. According to Hohenauer, the extremely low temperatures can cause skin burns and inhaling cryocabins — the vaporized liquid nitrogen in the tanks — can be life threatening in some cases.

“There are also a lot of contraindications for whole and partial body cryotherapy which should be taken into account,” Hohenauer added. For example, those with heart disease, respiratory issues or hypothyroidism should definitely avoid WBC.

For now, most health care providers are holding off on recommending WBC to patients until the science catches up. The body of literature on WBC is growing, and we may eventually find out cryotherapy is indeed an effective treatment for pain and soreness. Until we have more proof, though, it’s best to talk to your doctor and proceed with caution.

“Given the lack of evidence, expense and at least some risk of harm, I would not recommend it,” Shmerling said, adding, “Then again, if someone feels better doing it and has had no side effects, I would not discourage it.”